Various types and configurations of prosthetic heart valves are available or have been proposed for percutaneous transcatheter valve replacement procedures. In general, prosthetic heart valve designs attempt to replicate the functions of the native heart valve being replaced and thus will include valve leaflet-like structures mounted in some manner within an expandable stent frame, which in some instances is made of a shape memory material and construction. With such shape memory or self-expanding stent frames, the prosthetic heart valve is crimped to a desired size and held in a compressed delivery configuration within a retaining sheath, sleeve or capsule of a delivery catheter, for example, for delivery to a treatment site within the heart. In certain percutaneous transcatheter valve replacement procedures, the delivery catheter is introduced into a vessel, for example, the femoral artery or the brachial artery and tracked through the vasculature to the heart. Once the delivery catheter and more particularly the prosthetic heart valve are properly positioned with the native valve to be replaced, the retaining sheath, sleeve or capsule is retracted from the prosthetic heart valve to permit the stent frame to return to its expanded diameter for implantation within the native valve.
A delivery catheter must often navigate through tortuous anatomy as it is tracked through the vasculature to the treatment site within the heart, to include traversing the aortic arch. In the circumstance of a delivery catheter that houses a prosthetic heart valve compressed within a distal end of the retaining sheath, sleeve or capsule thereof, articulation of the catheter within the tortuous anatomy may cause a leading distal edge of the retaining sheath, sleeve or capsule to undesirably flex and/or separate from a distal tip of the delivery catheter, which is sometimes referred to as “fishmouthing.” The discontinuity or disconnection that results in an incomplete closure between the distal edge of the retaining sheath, sleeve or capsule and the distal tip, as well as the “fish-mouth”shape of the leading distal edge of the retaining sheath, sleeve or capsule may make tracking of the delivery catheter more difficult and also may result in the leading distal edge of the retaining sheath, sleeve or capsule catching on and/or damaging a wall of a vessel and/or structures of the heart as the delivery catheter is tracked onward to the delivery site within the heart. Additionally, the fish-mouthed leading end of the retaining sheath, sleeve or capsule can collect and/or dislodge emboli and/or can become damaged such that a reinforcing structure of the retaining sheath, sleeve or capsule becomes exposed creating greater concern that emboli and/or dissection of a vessel may occur.
In certain delivery systems, a clinician may have the ability to partially deploy the prosthetic heart valve, evaluate a position relative to the native annulus, and then reposition the prosthetic heart valve prior to full deployment if deemed necessary. Repositioning, in turn, requires the prosthetic heart valve first be re-compressed and re-located back within the retaining sheath, sleeve or capsule. In other words, the partially deployed prosthetic heart valve must be “recaptured” by the delivery catheter, and in particular be returned to within the retaining sheath, sleeve or capsule thereof. Often once the prosthetic heart valve is recaptured, the distal edge or end of the retaining sheath, sleeve or capsule may have experienced some permanent deformation and consequently have a greater inner diameter than before the initial deployment of the prosthetic heart valve. In such a situation, a gap may occur between the distal edge of the retaining sheath, sleeve or capsule and the distal tip, which may result in the delivery catheter having poor or reduced tracking capabilities after the recapture and to suffer from other deficiencies as noted above with regard to incomplete closure between the distal tip and the sheath, sleeve or capsule.
In light of the above, a need exists for a prosthetic heart valve delivery system that addresses the problems of fish-mouthing and/or other discontinuities/disconnections between a distal edge of a retaining sheath, sleeve or capsule and a distal tip of the delivery catheter that may occur during tracking and/or removal of the delivery catheter and/or during recapture of the prosthetic heart valve prior to full deployment of the prosthesis at a treatment site within the heart.